The electronic device fabrication industry requires various liquid chemicals as raw materials or precursors to fabricate integrated circuits and other electronic devices. This need arises from the requirement to dope semiconductors with various chemicals to provide the appropriate electrical properties in the semiconductor for transistors and gate oxides, as well as circuits requiring various metals, barrier layers, vias. Additionally, dielectric layers are needed for capacitors and interlayer dielectric requirements. Fabrication requiring subtractive technologies require resists, planarization chemistries and etchants.
All of the chemicals that are used in these applications are required in high purity conditions to meet the stringent requirements of the electronic fabrication industry imposed by the extremely fine line width and high device densities in current and future electronic devices being fabricated with those chemicals.
A part of the effort to provide high purity chemicals is the design and structure of the containers and systems which delivery such chemicals to the reactor or furnaces where the electronic devices are being fabricated. The purity of the chemicals can be no better than the containers in which they are stored and the systems through which they are dispensed.
In addition, it is important to monitor the quantity of high purity chemical available during its use in the electronic device fabrication process. Electronic devices are fabricated in quantities of several hundred at a time per semiconductor wafer, with the size of individual wafers being processed expected to be larger in future fabrication processes. This makes the value of the yield of electronic devices being processed on wafers very high, resulting in considerable cost if processing or fabrication occurs when the high purity chemical is unavailable inadvertently. Thus, the electronic fabrication industry has used monitoring of high purity chemical quantity a part of their scheme in their fabrication processes.
To address the issues of purity and monitoring of chemical quantity available for use, the industry has made various attempts to achieve those goals.
U.S. Pat. No. 5,199,603 discloses a container for organometallic compounds used in deposition systems wherein the container has inlet and outlet valves and a diptube for liquid chemical dispensing through the outlet. However, no level sensor is provided and the diptube terminates inside the container.
U.S. Pat. No. 5,562,132 describes a container for high purity chemicals with diptube outlet and internal float level sensor. The diptube is connected to the integral outlet valve. However, the diptube is not readily serviceable during refill or refurbishing of the container and the internal float level sensors are known particle generators for the high purity chemicals contained in the container.
U.S. Pat. No. 4,440,319 shows a container for beverages in which a diptube allows liquid dispensing based upon a pressurizing gas. The diptube may reside in a well to allow complete dispensing of the beverage. Level sense is not taught and the diptube is not readily removed or refurbished.
U.S. Pat. No. 4,053,085 discloses an arrangement for sealing a tube containing corrosive chemicals which uses two concentric washer seals of elastomeric materials. One seal is resilient and one is corrosion resistant. The use of metallic seals is not proposed.
U.S. Pat. No. 5,663,503 describes an ultrasonic sensor, which is known to be used to detect liquid presence in a vessel. Invasive and non-invasive sensors are described.
U.S. Pat. No. 6,077,356 shows a reagent supply vessel for chemical vapor deposition, which vessel has a sump cavity in which the liquid discharge dip tube terminates, as well as a liquid level sensor terminates. Ultrasonic sensors are contemplated (col. 6, line 37), but in that embodiment, the patent expressly teaches that the sensor does not utilize the sump for sensing operations (col. 6, line 38-43).
The shortcomings of the prior art in addressing the goals of purity and level sensing are overcome by the present invention, which provides high purity containment, ease of cleaning during refill or refurbishing and avoidance of contamination or particle generation during level sensing, level sensing with an external ultrasonic level sensor through a sump sized to accommodate a dip tube and a detection zone for the ultrasonic sensor, as well as avoidance of atmospheric contamination during any changeout or repair of the level sensing device. Other advantages of the present invention are also detailed below.
The present invention is a container for high purity chemicals comprising a shell with an external surface comprising a top surface, a side surface and a bottom surface, an orifice capable of being used as an inlet, an orifice capable of being used as an outlet, an ultrasonic level sensor affixed to the external bottom surface of said shell for determining the amount of high purity chemical in the container and a diptube removably connected to the outlet through which high purity chemical can be dispensed from the container, a sump in the bottom surface into which a lower end of the diptube terminates, the sump sized to accommodate the lower end of the dip tube and a detection zone for the ultrasonic level sensor to determine the amount of high purity chemical in the sump, wherein the ultrasonic level sensor is positioned adjacent the sump to at least determine the amount of chemical in the sump.
Preferably, the ultrasonic level sensor is located on a bottom surface of the external surface of the container below the sump.
In another embodiment, the present invention is a container for high purity chemicals having a metallic shell, a valved inlet, a valved outlet, an ultrasonic level sensor removeably affixed to an external bottom surface of said shell for determining the amount of high purity chemical in the container and a diptube removably connected to the outlet through which high purity chemical can be dispensed from the container by connection to a downstream high purity chemical delivery system, a sump in the bottom surface into which a lower end of the diptube terminates, the sump sized to accommodate the lower end of the dip tube and a detection zone for the ultrasonic level sensor to determine the amount of high purity chemical in the sump, the ultrasonic level sensor positioned below a portion of the sump unoccupied by the diptube.
Preferably, the level sensor is located below a portion of said sump and which is not below the diptube.
Preferably, the sump is sized to accommodate the lower end of the diptube and a detection zone for the ultrasonic level sensor that is of sufficient size to avoid level sensing interference of the diptube by the level sensor.
Preferably, the sump is below the plane of said bottom surface and comprises a portion of said bottom surface.
The present invention is also a method for determining the level of high purity chemical in a container of high purity chemical having a metallic shell with an external surface comprising a top surface, a side surface and a bottom surface, a valved inlet, a valved outlet, an ultrasonic level sensor affixed to the external bottom surface of the shell for determining the amount of high purity chemical in the container and a diptube connected to the outlet through which high purity chemical can be dispensed from the container, a sump in the bottom surface into which a lower end of the diptube terminates, comprising; positioning the ultrasonic level sensor below the sump, generating ultrasonic waves in the high purity chemical in the container, sensing the reflection of the generated ultrasonic waves by the sensor, and generating a signal proportional to the reflection.